1. Field of the Invention
The present invention relates to a zoom lens appropriate for a video camera, a digital still camera, a mobile information terminal (PDA: Personal Digital Assistance), and the like, and to an imaging apparatus.
2. Description of the Related Art
Imaging devices, such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor), used in imaging apparatuses, such as a digital still camera, became small in recent years. As the size of the imaging devices decreased, a demand for reducing the size of the whole imaging apparatus increased. To reduce the size of the whole imaging apparatus, it is desirable that the entire length of the lens is short and the lens system as a whole is small. In this case, it is desirable to structure the lens, considering not only the entire length of the lens during use (photography) but also the entire length of the lens in a stored non-use state (non-photography state). For example, it is desirable that the lens is structured in such a manner to be appropriate for a collapsible lens, which collapses into a camera body in non-photography state.
U.S. Pat. No. 6,975,461 (Patent Document 1), Japanese Unexamined Patent Publication No: 2005-326743 (Patent Document 2), and Japanese Unexamined Patent Publication No. 2008-310223 (Patent Document 3) disclose inventions related to four-group zoom lenses. The four-group zoom lens is composed of four lens groups having positive refractive power, negative refractive power, positive refractive power, and positive refractive power, which are sequentially arranged from the object side of the zoom lens.
The zoom lens disclosed in Patent Document 1 has a relatively high zooming magnification ratio of about five times, and the number of lenses is relatively small. However, the angle of view is about 60 degrees, which is not sufficiently wide. Further, since the power of each group is small, the amount of movement of each group is large, and it is difficult to reduce the size of the whole lens system.
Meanwhile, the zoom lens disclosed in Patent Document 2 has a relatively high zooming magnification ratio of about five times, and the angle of view is relatively wide. However, the amount of movement of the first lens group is large, and the length of the whole lens system at tele end is long. Therefore, it is difficult to reduce the size of the lens unit in a collapsed state.
Further, the zoom lens disclosed in Patent Document 3 has excellent compactness, because the number of lenses is small, and each lens group is thin. However, the angle of view is not sufficiently wide.